State the importance of the following:
$(1)$ Sebum
$(2)$ Counter current mechanism

We can produce a concentrated urine. This is facilitated by a special mechanism. Identify the mechanism.

The proximity between Henle's loop and vasa-recta as well as the counter-current in them help in maintaining an ...$A$... in molarity towards the inner medullary interstitium,i.e.,from ...$B$... $mOsmol \ L^{-1}$ in the cortex to about ...$C$... $mOsmol \ L^{-1}$ in the inner medulla. Here $A$,$B$,and $C$ refer to:

If $Henle's$ loop were absent from the mammalian nephron,which of the following is to be expected?

Compare the statements $A$ and $B$.
$\text{Statement } A$: When the urine moves through the descending limb,it becomes hypertonic,and as it passes through the ascending limb of Henle's loop,it becomes hypotonic.
$\text{Statement } B$: The descending limb is permeable to sodium ions,while the ascending limb is impermeable to sodium ions.

Indicate whether the following statement is true or false:
Henle's loop plays an important role in concentrating the urine.